In the kingdom of metals, zinc may not be as glittering as gold or silver, or as hard and heavy as steel,
but it is like the silent flow of industrial blood that supports modern civilization in all its forms. Purity
is the core code that gives zinc its unique power and value. From the “armor” that guards steel to the
energy that drives the future, high-purity zinc is quietly shaping our world with its irreplaceable role.
The Ruler of Purity: Measuring Zinc's Value Dimension
Zinc's purity is no simple numbers game. It directly determines the metal's physicochemical properties and
application boundaries. Industrially, purity grades are rigorous yardsticks:
Prime Western (PW): 99.0% to 99.9% pure, with small amounts of lead, cadmium, iron, etc. This is the most
common grade. This is the most common grade, is less costly, and is mainly used in hot-dip galvanizing (steel
corrosion protection), brass manufacturing, and die-cast alloys (e.g., door handles, automotive parts) where
there is a high tolerance for impurities.
High Grade (HG): Typically 99.95% pure or higher, with significantly lower impurity levels. It meets more demanding
needs such as composition control of certain special alloys, production of advanced chemicals (e.g. zinc oxide,
zinc powder) and some battery applications.
Special High Grade (SHG): Purity** ≥ 99.995%** (4N5), the pinnacle of commercial zinc purity. Critical impurities
such as lead, cadmium and iron are restricted to extremely low levels (often measured in ppm.) SHG zinc is the
cornerstone of cutting-edge applications and is valued for the superior performance that comes from its
unmatched purity.
Hardening purity: the road to precision for SHG zinc
Converting zinc ores, primarily sphalerite, to a high purity metal of 99.995% or more is a sophisticated process that
combines fire and water:
The foundation is laid in the primary smelting: the ore is enriched by flotation to obtain a zinc concentrate. The core
pyrometallurgical process is “roasting - leaching - electrolysis”:
Roasting: The concentrate is converted at high temperature into zinc oxide and sulphur dioxide (for acid production).
Leaching: The zinc oxide in the roasted sand is dissolved with dilute sulfuric acid to obtain a zinc sulfate solution
containing zinc and other metal ions.
Purification and decontamination: This is a key pretreatment to improve purity! Through precise control of pH value,
adding specific reagents (such as zinc powder) for multi-stage replacement precipitation, like a precise “molecular sieve”,
to gradually remove most of the impurity ions such as copper, cadmium, cobalt, nickel, arsenic and so on in the solution.
The depth of purification determines the upper limit of purity of the final product.
Electrolytic deposition: The purified pure zinc sulfate solution flows into the electrolytic tank. When direct current is
applied, zinc ions are reduced and precipitated on the aluminum cathode plate, forming a dense zinc plate (zinc cathode).
This is currently the dominant method for large-scale production of high-purity zinc.
Refining: To achieve the ultimate purity of SHG, electrolytic zinc sheets are subjected to refining:
Vacuum distillation: Taking advantage of the significant difference in volatility between zinc and impurity elements
(especially lead and cadmium), distillation is carried out in a high vacuum and at a specific temperature. The more
volatile impurities are preferentially gasified and separated, while the zinc vapors are recondensed in the condensation
zone into ultra-high purity zinc ingots. This is the core refining technology for the production of SHG zinc.
Zone melting (optional): For ultra-high purity zinc of laboratory grade or semiconductor grade (5N, 6N), zone melting
is used. By creating a narrow melting zone and moving it slowly, impurities are “driven” to one end of the ingot due to
the coagulation effect, which is repeated several times to obtain an extremely pure fraction.
The power of purity: SHG zinc's brightest stage
The ultimate elimination of 0.005% of impurities gives SHG zinc an irreplaceable “super power”:
The “soul” element of precision alloys: In the aerospace and high-end electronics fields, SHG zinc is a necessary raw material
for the manufacture of super-strong, super-tough, high-thermal-conductivity special alloys (such as some copper-zinc alloys
and nickel-silver alloys). Trace impurities can lead to sudden changes in alloy properties (e.g., increased brittleness,
decreased electrical conductivity), and SHG zinc ensures precise composition and reliable performance.
Flawless guarding of high-end coatings: In continuous galvanizing lines (e.g. for automotive and household appliances) or in
electroplating processes, SHG zinc results in extremely homogeneous, dense, bright and highly adhesive coatings. Reduced
impurities mean lower porosity, a leap in corrosion resistance and a better appearance.
The “pure source” of chemicals: The manufacture of highly reactive, high-quality zinc powders (for chemical reduction,
metallurgy, battery cathodes), ultra-pure zinc oxides (for high-end rubbers, ceramic glazes, sunscreens, electronic materials),
etc., has to start with SHG zinc to ensure the purity and reactivity of the final chemical.
Potential for the future of energy storage: At the forefront of the development of zinc-based batteries (e.g. zinc air batteries,
zinc ion batteries), SHG zinc plays a key role. High purity means lower side reactions, higher Coulombic efficiency, longer cycle
life and more stable performance, and it is one of the core materials for improving the performance of the next generation
of safe, environmentally friendly and low-cost batteries.
Behind the scenes in semiconductors and photovoltaics: In the manufacture of compound semiconductors (e.g. ZnSe, ZnS for
infrared windows, lasers) and sputtering targets, the purity of the base zinc material is extremely stringent (often 5N or higher),
and SHG zinc is a necessary stepping stone to these cutting-edge applications.
Beyond purity: sustainability considerations
The production of high-purity zinc is an energy- and resource-intensive process. The industry is moving aggressively:
Recycling: Zinc has excellent recyclability. From galvanized steel and brass scrap to zinc slag and soot, efficient recycling networks
put zinc scrap back into the furnace, where it can be properly refined to achieve high purity again, significantly reducing primary
mineral consumption and environmental impact.
Process Optimization: Continuous improvement of smelting and refining processes, enhancement of energy efficiency, reduction
of emissions, and enhancement of the comprehensive recovery of valuable metals in waste water and slag.
Conclusion: A hidden but great cornerstone
The purity of zinc metal, especially the 99.995% SHG zinc, is often hidden behind the scenes, but it is the silent force that
supports the precision operation of modern industry and drives technological innovation. It is born from ancient ores, purified
through thousands of refinements, and eventually transformed into the armor of steel, the veins of electronics, the catalyst
of chemistry, and even the carrier of future energy. The relentless pursuit of purity not only defines the value of zinc, but also
reflects the human industrial civilization's exploration and reverence for the limits of materials. In countless key nodes related
to performance, reliability and innovation, high-purity zinc, the “invisible champion”, has always quietly played an irreplaceable
role as a cornerstone.